HT45F12
8-Bit Flash MCU with Op Amps & Comparators
Selectingꢀwhetherꢀtheꢀlowꢀorꢀhighꢀspeedꢀoscillatorꢀisꢀusedꢀasꢀtheꢀsystemꢀoscillatorꢀisꢀimplementedꢀ
usingꢀtheꢀHLCLKꢀbitꢀandꢀLCKS2~LCKS0ꢀbitsꢀinꢀtheꢀSYSMODꢀregisterꢀandꢀasꢀtheꢀsystemꢀclockꢀ
canꢀbeꢀdynamicallyꢀselected.ꢀTheꢀactualꢀsourceꢀclockꢀusedꢀforꢀeachꢀofꢀtheꢀhighꢀspeedꢀandꢀlowꢀspeedꢀ
oscillatorsꢀisꢀchosenꢀviaꢀconfigurationꢀoptions.ꢀTheꢀfrequencyꢀofꢀtheꢀslowꢀspeedꢀorꢀhighꢀspeedꢀ
systemꢀclockꢀisꢀalsoꢀdeterminedꢀusingꢀtheꢀHLCLKꢀbitꢀandꢀLCKS2~LCKS0ꢀbitsꢀinꢀtheꢀSYSMODꢀ
register.ꢀNoteꢀthatꢀtwoꢀoscillatorꢀselectionsꢀmustꢀbeꢀmadeꢀnamelyꢀoneꢀhighꢀspeedꢀandꢀoneꢀlowꢀspeedꢀ
systemꢀoscillators.ꢀItꢀisꢀnotꢀpossibleꢀtoꢀchooseꢀaꢀno-oscillatorꢀselectionꢀforꢀeitherꢀtheꢀhighꢀorꢀlowꢀ
speedꢀoscillator.
External Crystal/Ceramic Oscillator – HXT
TheꢀExternalꢀCrystal/CeramicꢀSystemꢀOscillatorꢀisꢀoneꢀofꢀtheꢀhighꢀfrequencyꢀoscillatorꢀchoices,ꢀ
whichꢀisꢀselectedꢀviaꢀconfigurationꢀoption.ꢀForꢀmostꢀcrystalꢀoscillatorꢀconfigurations,ꢀtheꢀsimpleꢀ
connectionꢀofꢀaꢀcrystalꢀacrossꢀOSC1ꢀandꢀOSC2ꢀwillꢀcreateꢀtheꢀnecessaryꢀphaseꢀshiftꢀandꢀfeedbackꢀforꢀ
oscillation,ꢀwithoutꢀrequiringꢀexternalꢀcapacitors.ꢀHowever,ꢀforꢀsomeꢀcrystalꢀtypesꢀandꢀfrequencies,ꢀ
toꢀensureꢀoscillation,ꢀitꢀmayꢀbeꢀnecessaryꢀtoꢀaddꢀtwoꢀsmallꢀvalueꢀcapacitors,ꢀC1ꢀandꢀC2.ꢀUsingꢀaꢀ
ceramicꢀresonatorꢀwillꢀusuallyꢀrequireꢀtwoꢀsmallꢀvalueꢀcapacitors,ꢀC1ꢀandꢀC2,ꢀtoꢀbeꢀconnectedꢀasꢀ
shownꢀforꢀoscillationꢀtoꢀoccur.ꢀTheꢀvaluesꢀofꢀC1ꢀandꢀC2ꢀshouldꢀbeꢀselectedꢀinꢀconsultationꢀwithꢀtheꢀ
crystalꢀorꢀresonatorꢀmanufacturer’sꢀspecification.
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Crystal/Resonator Oscillator – HXT
Crystal Oscillator C1 and C2 Values
Crystal Frequency
1ꢄMHz
C1
0ꢀF
C2
0ꢀF
8MHz
0ꢀF
0ꢀF
4MHz
0ꢀF
0ꢀF
1MHz
100ꢀF
100ꢀF
Note: C1 and Cꢄ values aꢃe foꢃ guidance only.
Crystal Recommended Capacitor Values
Rev. 0.00
34
�eꢀteꢁꢂeꢃ ꢄꢅꢆ ꢄ01ꢄ
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
